Three primary reasons were:Admiral Valdemar wrote:Wasn't Curiosity's used down to it being just too damn heavy to drop with parachutes and get a decent landing? It would be cool if they added dust effects for landings, though. Scorch marks, dust, shockwaves and Max Q effects would all add to the eye candy.
1. Weight of the rover itself, which precluded an airbag system, since they don't scale linearly, and a parachute because Mars atmosphere is too thin to allow you to use practical ones. MSL's drag chute was already pretty gigantic, and it wasn't expected to actually serve for terminal landing.
2. Weight limitations of the Centaur, which precluded a classic powered landing, since a big enough landing shell (think Lunokhod) would weigh just too damn much to fit.
3. Terrain: both airbags and a capsule run a chance of landing in rough terrain and being unable to deploy the rover ; The skycrane, on the other hand, could land MSL safely even on a significant incline! This actually combines with weight of the rover itself.